1. Field of the Invention
This invention is directed to a device for raising or lowering tubing, cable, rods or tubular structure for example, but not limited to, within a well. Such devices are commonly called snubbing assemblies or snubbers when used in conjunction with a well. This invention may be used in any industry or application where there is a need to raise and lower a tubing, cable, or rod in a controlled manner.
2. Description of Related Art
The purpose of a snubbing unit is to run tubing or pipe into and out of the well bore with the well bore having a greater pressure than the normal atmospheric pressure. In most cases during drilling or completion of an oil and gas well, if the well pressure exceeds the weight of the tubing or pipe the tubing could be ejected from the well. This pipe ejection is referred to as a blow out. In Order to prevent this ejection the oil and gas industry uses two methods for controlling the well. One method is to use a weighting to control it and the other is to complete the well using live well procedures i.e. snubbing. Recently the oil and gas industry has begun to better understand that the use of drilling mud/weighting materials with a high enough weight to balance the well's natural pressure can cause damage to the formation thus inhibiting the productivity of the well. Therefore the practice of insertion of the tubing into and out of the well bore under pressure (snubbing) has increased.
The current method used for this under balanced insertion of the tubing, referred to as snubbing, is a process that uses cables, chains or hydraulic cylinders and two sets of inverted slips to push the tubing into and out of the well bore under pressure. This is done in a hand over hand process where one set of the slips are closed around the tubing and then pulled against the opposing force of the well. This load or well bore force is then transferred through the pipe and then to the slips. The pipe is held stationary by one set of slips that are tied to the well while the other set of slips travel up and down the pipe. The traveling slips grab the tubing or pipe and the slips are then draw downward. Once the load of the tubing or pipe is transferred to these slips, the stationary slips are opened and the pipe is pushed into the wellbore through either a stripping rubber or a set of blow out preventer (BOP) rams, both of which are designed to seal around the outside of the pipe or tubing keeping the well bore pressure contained. Once the traveling set of slips has reached its lowest travel point, the bottom or stationary set of slips are closed and the traveling set of slips are opened and raised to take another bite. The process is then repeated until the length of the pipe can be fully inserted into the well. This process is very slow and requires a well organized movement between the two sets of slips.
These snubbing operations can be broken into two categories. The first one is referred to as a stand-alone snubbing unit. This unit is completely self contained and needs no assistance to handle the tubing in and out of the well bore. It has two sets of stationary slips and two sets of traveling slips. One set of these slips is to hold and transfer the load of the tubing when the pipe is being snubbed and the other set holds the pipe when it is in heavy position. This allows the snubbing unit to handle the pipe in both positive and negative load positions.
The other type of snubbing unit is referred to as a rig assist unit. In this case the snubbing unit is used to assist a work-over in running of the pipe. Once the snubbing unit has pushed the tubing into the well and the weight of the pipe is enough to overcome the pressure from the well the work-over rig takes over and finishes running the tubing into the well bore. The reason for this is the work-over rig can run the tubing into the well bore much faster than a snubbing unit that has to use the hand over hand operations. Because the snubbing unit is not equipped with slips to handle the pipe in the heavy position, the work over has to be used to assist this unit in running the pipe. This motion requires great coordination between the snubbing operator and the work over rig operator. Any mistake can result in a blow out or the accidental release of the tubing from the wellbore.
Both of these types of units are very slow and require great coordination to run the pipe with any speed. This complexity of operation provides a need for equipment and operations that are much less complex and safer that the current operations. The current invention does just that.